THIS INVENTION relates to an automotive diagnostic aid or control device for petrol-driven, electronic fuel-injected (EFI) engines.
Most modern petrol driven production cars are fitted with catalytic converters and an engine management system which electronically controls the air/fuel ratio (AFR), incorporating the use of an oxygen sensor and operating in what is known as a xe2x80x9cclosed loopxe2x80x9d mode. Oxygen readings are transmitted to an engine management computer (ECU) along with various other parameters, and adjustments are electronically made to provide repeated self-correction of the AFR. This is intended to cause the engine to run at perfect combustion with an AFR of 14.75:1 (also known as Factor 1).
This closed loop mode of operation can, however, render many faults difficult to diagnose. For example, a vehicle with an inlet manifold air leak would idle very erratically as the ECU attempts to compensate by adjusting the amount of fuel fed to the engine, based on incorrect readings taken from an air flow meter which is situated before the point of the air leak. This makes traditional diagnostic methods difficult as, in most case, it is necessary to make the engine stable before commencing common test procedures.
One approach to achieve stabilised running before curing a fault such as this is to take the vehicle out of closed loop mode and force it to run in an open loop condition by introducing a means for controlling the pulsing of the fuel injectors at a stabilised (non-fluctuating) rate. To achieve this by means of some kind of fuel controlling device and then to introduce a method of varying the pulses, the amount of fuel injected into the engine can be manually controlled. With the aid of an exhaust gas analyser many more tests can be performed such as catalytic converter testing when an engine is not running at Factor 1, by forcing it to do so and then monitoring the emissions from the exhaust.
Patent specification U.S. Pat. No. 5,214,582 describes an engine diagnostic/control system which is adapted to receive the sequential control signal from the ECU and reproduce it, without modification, while the engine is running. Alternatively, when the engine is not running, it may ignore the signal from the ECU while testing the injectors and other engine components for their operability. The device described in this document cannot operate in a open loop mode i.e. to take the control signal and to modify it thus to operate the injectors according to a modified signal.
Patent specification U.S. Pat. No. 5,107,426 is a further injection and ignition tester and is adapted for connection to an engine injector to test its operability. The device is connected in parallel to the ECU not between it and the injectors.
According to the present invention a diagnostic/control device for fuel injected internal combustion engines comprises a control system having means for electrical connection directly to at least one fuel injector of an engine and to an engine management computer, and further means to actuate said at least one injector independently of the engine management computer.
Further according to the present invention there is provided a method of testing fuel injected internal combustion engines comprising the steps of providing a control system, electrically connecting the control system directly to at least one fuel injector of an engine in place of an engine management computer normally connected thereto, connecting the control system also to the engine management computer, and causing the control system to actuate said at least one injector independently of the engine management computer.